1. Technical Field
The present invention relates to a vehicle comprising (including, but not limited to) a first and a second frame section connected by an articulation (articulated connection), in which a positioning arrangement is capable of orienting the frame sections in relation to one another about the longitudinal axis of the vehicle, as well as a method for effecting the same.
2. Background
Articulated vehicles are familiar to the person skilled in the art, such as found in the example of British Patent Publication, GB 2258437, which is expressly incorporated herein by reference. An articulated vehicle has a frame that is divided into a front and a rear frame half, which are connected by way of an axially aligned cylindrical bearing. The articulation consists, for example, of a cylinder (fixed to the one frame half) in which a pin (fixed in the second frame half) is supported. The articulation may also be of the sluing ring bearing type. On an articulated vehicle, the frame halves can rotate in relation to one another along the axis of rotation of the bearing in the longitudinal direction of the vehicle. Exemplary articulated vehicles include dump trucks, a wheeled loaders and forklift trucks. A significant advantage of utilizing an articulated connection is that the wheels of the vehicle obtain better ground contact on uneven surfaces. A major disadvantage, however, is that the stability of the vehicle is reduced. For a dump truck, reduced stability is a disadvantage, among other things, when the vehicle is to be driven at high speed. For a wheeled loader or a fork-lift truck, reduced stability is a disadvantage, among other things, in the case of heavy and/or high lifting. There are therefore instances where it is desirable to lock the front frame half together with the rear frame half in order to increase the stability of the vehicle.
One method that has been proposed for locking the frame halves to one another is to use a locking pin that is inserted into a corresponding hole. A disadvantage of this solution is that the vehicle must be standing level in order to be able to insert the locking pin in position. Another disadvantage is that this makes the locking entirely rigid without any resilient characteristics and places an unnecessarily high load on the vehicle when driving over broken ground. There is also a greater risk of a rigid vehicle overturning. A locking arrangement with such a locking pin is described, for example, in GB 1166219, JP 58164481, GB 2258437, SU 958199, U.S. Pat. Nos. 5,806,870 and 4,079,955.
Another solution-method that has been proposed is to lock the frame halves by means of a brake arrangement in the form of a disc or drum brake. A disadvantage with this method is again that the vehicle must be standing level when the brake is applied in order that the vehicle will be locked in a position in which the frame halves lie in one plane with one another. Another disadvantage with this method of locking is that there is nothing to indicate that the frame halves are lying in one plane. If the frame halves are locked when they are not lying in one plane, this will result in inferior driving characteristics and uneven weight distribution. A locking arrangement in which the locking is achieved with a brake arrangement is described, for example, in U.S. Pat. No. 4,235,308 and DE 2701813.
Another type of brake arrangement is described in U.S. Pat. No. 4,353,572 in which two hydraulic cylinders that are connected to one another are used as a locking arrangement. In order to lock the articulation, the oil flow between the cylinders is shut off by means of a valve, the valve being opened if a rotatable articulation is required. A major disadvantage with this solution is that it does not permit large angles of rotation between the frame halves; something that can be catastrophic when there is a risk of the vehicle overturning. Another disadvantage is again that the vehicle must be standing level when the locking is applied in order that the vehicle will be locked in a position in which the frame halves lie in one plane with one another. Yet another disadvantage with this method of locking is that there is nothing to indicate that the frame halves lie in one plane.